Use fastpos.h when encoding LZMA dictionary size in

Filter Flags encoder.

diff --git a/src/liblzma/common/filter_flags_encoder.c b/src/liblzma/common/filter_flags_encoder.c
index d8f260a..2d11dd3 100644 (file)
--- a/src/liblzma/common/filter_flags_encoder.c
+++ b/src/liblzma/common/filter_flags_encoder.c
@@ -19,6 +19,7 @@
 
 #include "common.h"
 #include "lzma_encoder.h"
+#include "fastpos.h"
 
 
 /// \brief      Calculates the size of the Filter Properties field
@@ -204,35 +205,32 @@ properties_lzma(uint8_t *out, size_t *out_pos, size_t out_size,
 
        // Dictionary flags
        //
-       // Dictionary size is encoded using six bits of
-       // which one is mantissa and five are exponent.
+       // Dictionary size is encoded using similar encoding that is used
+       // internally by LZMA.
        //
-       // There are some limits that must hold to keep
-       // this coding working.
-#      if LZMA_DICTIONARY_SIZE_MAX > UINT32_MAX / 2
-#              error LZMA_DICTIONARY_SIZE_MAX is too big.
-#      endif
+       // This won't work if dictionary size can be zero:
 #      if LZMA_DICTIONARY_SIZE_MIN < 1
 #              error LZMA_DICTIONARY_SIZE_MIN cannot be zero.
 #      endif
 
+       uint32_t d = options->dictionary_size;
+
        // Validate it:
-       if (options->dictionary_size < LZMA_DICTIONARY_SIZE_MIN
-                       || options->dictionary_size > LZMA_DICTIONARY_SIZE_MAX)
+       if (d < LZMA_DICTIONARY_SIZE_MIN || d > LZMA_DICTIONARY_SIZE_MAX)
                return LZMA_HEADER_ERROR;
 
-       if (options->dictionary_size == 1) {
-               // Special case
-               out[*out_pos] = 0x00;
-       } else {
-               // TODO This could be more elegant.
-               uint32_t i = 1;
-               while (((2 | ((i + 1) & 1)) << ((i - 1) / 2))
-                               < options->dictionary_size)
-                       ++i;
-               out[*out_pos] = i;
-       }
-
+       // Round up to to the next 2^n or 2^n + 2^(n - 1) depending on which
+       // one is the next:
+       --d;
+       d |= d >> 2;
+       d |= d >> 3;
+       d |= d >> 4;
+       d |= d >> 8;
+       d |= d >> 16;
+       ++d;
+
+       // Get the highest two bits using the proper encoding:
+       out[*out_pos] = get_pos_slot(d) - 1;
        ++*out_pos;
 
        return LZMA_OK;